This fellowship would support collaborative research with Stanislas Denaene on the nature and development of number representations in human infants, young children, and human adults. Adults' number representations will be assessed using both behavioral and neuroimaging techniques (fMRI, ERPs) to test the hypothesis that mature representations of number depend on two distinct subsystems: an exact small-number system and an approximate large-number system, that are coordinated by natural language. Children's number representations will be assessed using behavioral and neuroimaging techniques (ERPs) to test the hypothesis that children assemble the same two systems in learning number words and verbal counting. Finally, infants' number representations will be assessed using behavioral and neuroimaging techniques (ERPs and optical imaging) in an initial effort to chart the developmental origins of these two systems. The research will be conducted. during two visits by Spelke to Dehaene's lab in Paris: an initial visit of 10 months (from 11/O1/00 to 8/31/01). and a follow-up visit of 2 months (from 07/01/02 torn 08/31/02)